Basic mouse scroll-wheel event (#222)

add simple mouse wheel event + example

crates/bevy_input/src/lib.rs

@@ -11,7 +11,7 @@ pub mod prelude {
 
 use bevy_app::prelude::*;
 use keyboard::{keyboard_input_system, KeyCode, KeyboardInput};
-use mouse::{mouse_button_input_system, MouseButton, MouseButtonInput, MouseMotion};
+use mouse::{mouse_button_input_system, MouseButton, MouseButtonInput, MouseMotion, MouseWheel};
 
 use bevy_ecs::IntoQuerySystem;
 
@@ -24,6 +24,7 @@ impl Plugin for InputPlugin {
         app.add_event::<KeyboardInput>()
             .add_event::<MouseButtonInput>()
             .add_event::<MouseMotion>()
+            .add_event::<MouseWheel>()
             .init_resource::<Input<KeyCode>>()
             .add_system_to_stage(
                 bevy_app::stage::EVENT_UPDATE,

crates/bevy_input/src/mouse.rs

@@ -26,6 +26,21 @@ pub struct MouseMotion {
     pub delta: Vec2,
 }
 
+/// Unit of scroll
+#[derive(Debug, Clone)]
+pub enum MouseScrollUnit {
+    Line,
+    Pixel,
+}
+
+/// A mouse scroll wheel event, where x represents horizontal scroll and y represents vertical scroll.
+#[derive(Debug, Clone)]
+pub struct MouseWheel {
+    pub unit: MouseScrollUnit,
+    pub x: f32,
+    pub y: f32,
+}
+
 /// State used by the mouse button input system
 #[derive(Default)]
 pub struct MouseButtonInputState {

crates/bevy_winit/src/lib.rs

@@ -4,7 +4,7 @@ pub use winit_windows::*;
 
 use bevy_input::{
     keyboard::KeyboardInput,
-    mouse::{MouseButtonInput, MouseMotion},
+    mouse::{MouseButtonInput, MouseMotion, MouseScrollUnit, MouseWheel},
 };
 
 use bevy_app::{prelude::*, AppExit};
@@ -119,6 +119,26 @@ pub fn winit_runner(mut app: App) {
                         state: converters::convert_element_state(state),
                     });
                 }
+                WindowEvent::MouseWheel { delta, .. } => match delta {
+                    event::MouseScrollDelta::LineDelta(x, y) => {
+                        let mut mouse_wheel_input_events =
+                            app.resources.get_mut::<Events<MouseWheel>>().unwrap();
+                        mouse_wheel_input_events.send(MouseWheel {
+                            unit: MouseScrollUnit::Line,
+                            x,
+                            y,
+                        });
+                    }
+                    event::MouseScrollDelta::PixelDelta(p) => {
+                        let mut mouse_wheel_input_events =
+                            app.resources.get_mut::<Events<MouseWheel>>().unwrap();
+                        mouse_wheel_input_events.send(MouseWheel {
+                            unit: MouseScrollUnit::Pixel,
+                            x: p.x as f32,
+                            y: p.y as f32,
+                        });
+                    }
+                },
                 _ => {}
             },
             event::Event::DeviceEvent { ref event, .. } => {

examples/input/mouse_input_events.rs

@@ -1,5 +1,5 @@
 use bevy::{
-    input::mouse::{MouseButtonInput, MouseMotion},
+    input::mouse::{MouseButtonInput, MouseMotion, MouseWheel},
     prelude::*,
     window::CursorMoved,
 };
@@ -17,6 +17,7 @@ struct State {
     mouse_button_event_reader: EventReader<MouseButtonInput>,
     mouse_motion_event_reader: EventReader<MouseMotion>,
     cursor_moved_event_reader: EventReader<CursorMoved>,
+    mouse_wheel_event_reader: EventReader<MouseWheel>,
 }
 
 /// This system prints out all mouse events as they come in
@@ -25,6 +26,7 @@ fn print_mouse_events_system(
     mouse_button_input_events: Res<Events<MouseButtonInput>>,
     mouse_motion_events: Res<Events<MouseMotion>>,
     cursor_moved_events: Res<Events<CursorMoved>>,
+    mouse_wheel_events: Res<Events<MouseWheel>>,
 ) {
     for event in state
         .mouse_button_event_reader
@@ -40,4 +42,8 @@ fn print_mouse_events_system(
     for event in state.cursor_moved_event_reader.iter(&cursor_moved_events) {
         println!("{:?}", event);
     }
+
+    for event in state.mouse_wheel_event_reader.iter(&mouse_wheel_events) {
+        println!("{:?}", event);
+    }
 }